A photo taken from the Facebook page of Quang Nguyen Van shows two men putting a cigarette in the mouth of a gray-shanked douc langur. The one on the left is in an army uniform, and it is unclear if the monkey is alive at this point.

It is unclear if they were just insensitive and weird or sadistic. But a group of young men now face possible criminal charges after posting photos of themselves sticking cigarettes in the mouths of an endangered monkey seemingly already dead and doing other bizarre things on Facebook.

But in some of the 12 photos Quang Nguyen Van of Quang Nam Province uploaded this week, he and his friends have another monkey tied with rope. It is alive and it is not clear what they did with it.

Then there are photos of the boys dunking one of the animals in boiling water to get rid of its fur, and other photos of the men disemboweling the animals.

One of them, grinning, poses with the head of one of the langurs, while others pose with the two animals' skulls, meaning they surely killed at least one of them.

After the photos spread on the Internet, there were thousands of comments from people expressing shock and anger. Many called on the police to investigate the killing of the endangered animals and punish the people in the photos.

Online newspaper VnExpress quoted Prof Vo Quy of the Vietnam National University's Natural Resources and Environment Research Center as saying the monkeys may have been gray-shanked douc langurs (Pygathrix cinerea).

It is a species native to the provinces of Quang Nam, Quang Ngai, Binh Dinh, Kon Tum, and Gia Lai.

Tran The Lien, chief of the Nature Conservation Division, said the acts were "unacceptable" and must be condemned.

"Whether the men are civilians or soldiers, they must face criminal charges," he said.

Phan Tuan, chief of the Quang Nam Forest Management Department, told Tuoi Tre he has asked all forest management offices in the province to study the photos and information provided to find out where and when the slaughter took place and identify the men.

"The police have been asked to investigate this case; the men will be charged with killing endangered animals," he said.